Poly(aryl ether ketones) are a known class of engineering polymers. Several poly(aryl ether ketones) are highly crystalline with melting points above 300.degree. C. Two of these crystalline poly(aryl ether ketones) are commercially available and are of the following structure: ##STR1##
Over the years, there has been developed a substantial body of patent and other literature directed to formation and properties of poly(aryl ethers). Some of the earliest work, such as by Bonner, U.S. Pat. No. 3,065,205, involves the electrophilic aromatic substitution (e.g. FriedelCrafts catalyzed) reaction of aromatic diacylhalides with unsubstituted aromatic compounds such as diphenyl ether. The evolution of this class to a much broader range of PAE's was achieved by Johnson et al., Journal of Polymer Science, A-1, Vol. 5, 1967, pp. 2415-2427; Johnson et al., U.S. Pat. Nos. 4,107,837 and 4,175,175. Johnson et al. show that a very broad range of PAE can be formed by the nucleophilic aromatic substitution (condensation) reaction of an activated aromatic dihalide and an aromatic diol. By this method, Johnson et al. created a host of new PAE's including a broad class of poly(aryl ether ketones), hereinafter called "PAEK".
In recent years, there has developed a growing interest in PAEK's as evidenced by Dahl, U.S. Pat. No. 3,953,400; Dahl et al. U.S. Pat. No. 3,956,240; Dahl, U.S. Pat. No. 4,247,682; Rose et al., U.S. Pat. No. 4,320,224; Maresca, U.S. Pat. No. 4,339,568; Atwood et al., Polymer, 1981, Vol. 22, August, pp. 1096-1103; Blundell et al., Polymer, 1983, Vol. 24, August, pp. 953-958; Atwood et al., Polymer Preprints, 20, No. 1, April 1979, pp. 191-194; and Rueda et al., Polymer Communications, 1983, Vol. 24, September, pp. 258-260. In the early-to-mid 1970's, Raychem Corp. commercially introduced a PAEK called Stilan.sup..TM., a polymer whose acronym is PEK, each ether and keto group being separated by 1,4-phenylene units. In 1978, Imperial Chemical Industries PLC (ICI), commercialized a PAEK under the trademark Victrex PEEK. As PAEK is the acronym of poly(aryl ether ketone), PEEK is the acronym of poly(ether ether ketone) in which the 1,4-phenylene units in the structure are assumed.
Thus, PAEK's are well known; they can be synthesized from a variety of starting materials, and they can be made with different melting temperatures and molecular weights. The PAEK's are crystalline, and, as shown by the Dahl and Dahl et al. patents, supra, at sufficiently high molecular weights they can be tough, i.e., they exhibit high values (&gt;50 ft-lbs/in.sup.2) in the tensile impact test (ASTM D-1822). They have potential for a wide variety of uses, but because of the significant cost to manufacture them, they are expensive polymers. Their favorable properties class them in the upper bracket of engineering polymers.
PAEK's may be produced by the Friedel-Crafts catalyzed reaction of aromatic diacylhalides with unsubstituted aromatic compounds such as diphenyl ether as described in, for example, U.S. Pat. No. 3,065,205. These processes are generally inexpensive processes; however, the polymers produced by these processes have been stated by Dahl et al., supra. to be brittle and thermally unstable. The Dahl patents, supra, allegedly depict more expensive processes for making superior PAEK's by Friedel-Crafts catalysis. In contrast, PAEK's such as PEEK made by nucleophilic aromatic substitution reactions are produced from expensive starting fluoro monomers, and thus would be classed as expensive polymers.
These poly(aryl ether ketones) exhibit an excellent combination of properties, i.e., thermal and hydrolytic stability, high strength and toughness, wear and abrasion resistance and solvent resistance. Thus, articles molded from poly(aryl ether ketones) have utility where high performance is required.
The melting point requirements of these materials vary with their particular applications. A characteristic facet of PAEK technology is that the crystalline melting point can be fairly accurately determined from the ether-to-ketone ratio in the polymer. As the ratio goes up, the melting point (T.sub.m) goes down. The change of the ether-to-keto ratio can be achieved by increasing the ether-containing and/or forming component in the polymer manufacture at the expense of the keto-containing component and vice versa. The tools for doing this are well within the capabilities of the skilled chemist, knowledgeable of the techniques of electrophilic and nucleophilic aromatic substitution reactions. Moreover, the displacement of these groups along the linear chain of the polymer is not narrowly critical to achieving the T.sub.m and T.sub.g properties. The practical problem encountered with this approach, however, is that for each poly(aryl ether ketone) with a given melting point, a separate preparative scheme utilizing well-defined raw materials is required. This is obviously highly impractical.
A much simpler and a much more desirable approach consists in the ability to blend two polymers to obtain a tough poly(aryl ether ketone) with one T.sub.g and one melting point as required for the particular application.
Polymer miscibility is virtually impossible to predict a priori; a very small variation in structure may lead to a totally different solubility behavior. Hence, the solubility properties discovered by the inventors are unexpected and unique. A brief discussion of polymer miscibility, which will illustrate the above, follows.
In the field of miscibility or compatibility of polymer blends, the art has found predictability to be unattainable, even though considerable work on the matter has been done. According to authorities:
(A) "It is well known that compatible polymer blends are rare." Wang and Cooper, Journal of Polymer Science, Polymer Physics Edition, Vol. 21, p. 11 (1983). PA1 (B) "Miscibility in polymer-polymer blends is a subject of widespread theoretical as well as practical interest currently. In the past decade or so, the number of blend systems that are known to be miscible has increased considerably. Moreover, a number of systems have been found that exhibit upper and lower critical solution temperatures, i.e., complete miscibility only in limited temperature ranges. Modern thermodynamic theories have had limited success to date in predicting miscibility behavior in detail. These limitations have spawned a degree of pessimism regarding the likelihood that any practical theory can be developed that can accommodate the real complexities that nature has bestowed on polymer-polymer interactions." Kambour, Bendler, Bopp, Macromolecules, 1983, 16, 753. PA1 (C) "The vast majority of polymer pairs form two-phase blends after mixing as can be surmised from the small entropy of mixing for very large molecules. These blends are generally characterized by opacity, distinct thermal transitions, and poor mechanical properties. However, special precautions in the preparation of two-phase blends can yield composites with superior mechanical properties. These materials play a major role in the polymer industry, in several instances commanding a larger market than either of the pure components." Olabisi, Robeson, and Shaw; Polymer-Polymer Miscibility, 1979, published by Academic Press, New York, N.Y., p. 7. PA1 (D) "It is well known that, regarding the mixing of thermoplastic polymers, incompatibility is the rule and miscibility or even partial miscibility is the exception. Since most thermoplastic polymers are immiscible with other thermoplastic polymers, the discovery of a homogeneous mixture or partially miscible mixture of two or more thermoplastic polymers is, indeed, inherently unpredictable with any degree of certainty." P. J. Flory, Principles of Polymer Chemistry, Cornell University Press, 1953, Chapter 13, p. 555. Younes, U.S. Pat. No. 4,371,672. PA1 (E) "The study of polymer blends has assumed an ever increasing importance in recent years and the resulting research effort has led to the discovery of a number of miscible polymer combinations. Complete miscibility is an unusual property in binary polymer mixtures which normally tend to form phase-separated systems. Much of the work has been of a qualitative nature, however, and variables such as molecular weight and conditions of blend preparation have often been overlooked. The criteria for establishing miscibility are also varied and may not always all be applicable to particular systems." Saeki, Cowie and McEwen, Polymer, 1983, Vol. 25, January, p. 60. PA1 "The most commonly used method for establishing miscibility in polymer-polymer blends or partial phase mixing in such blends is through determination of the glass transition (or transitions) in the blend versus those of the unblended constituents. A miscible polymer blend will exhibit a single glass transition between the Tg's of the components with a sharpness of the transition similar to that of the components. In cases of borderline miscibility, broadening of the transition will occur. With cases of limited miscibility, two separate transitions between those of the constituents may result, depicting a component 1-rich phase and a component 2-rich phase. In cases where strong specific interactions occur, the Tg may go through a maximum as a function of concentration. The basic limitation of the utility of glass transition determinations in ascertaining polymer-polymer miscibility exists with blends composed of components which have equal or similar (&lt;20.degree. C. difference) Tg's, whereby resolution by the techniques to be discussed of two Tg's is not possible." PA1 "Perhaps the most unambiguous criterion of polymer compatibility is the detection of a single glass transition whose temperature is intermediate between those corresponding to the two component polymers." PA1 (1) a substantially equimolar mixture of PA1 (2) at least one halophenol, in which in the dihalobenzenoid compound or halophenol, the halogen atoms are activated by --CO-- groups ortho or para thereto, with a mixture of sodium carbonate or bicarbonate and a second alkali metal carbonate or bicarbonate, the alkali metal of said second alkali metal carbonate or bicarbonate having a higher atomic number than that of sodium, the amount of said second alkali metal carbonate or bicarbonate being such that there are 0.001 to 0.2 grams atoms of said alkali metal of higher atomic number per gram atom of sodium, the total amount of alkali metal carbonate or bicarbonate being such that there is at least one alkali metal atom for each phenol group present, and thereafter separating the polymer from the alkali metal halide. PA1 (1) a mixture of substantially equimolar amounts of PA1 wherein --Ar"-- is a divalent aromatic radical and H is an aromatically bound hydrogen atom, which compound is polymerizable with at least one diacyl halide of (1)(a), or PA1 (2) at least one aromatic monacyl halide of the formula: EQU H--Ar"--COY PA1 where --Ar"-- is a divalent aromatic radical, H is an aromatically bound hydrogen atom, and Y and COY are as defined above, which monoacyl halide is self-polymerizable, or PA1 (3) a combination of (1) and (2) are reacted in the presence of a fluoroalkane sulphonic acid.
Thus, miscible polymer blends are not common. The criteria for determining whether or not two polymers are miscible are now well established. According to Olabisi et al., Polymer-Polymer Miscibility, 1979, published by Academic Press, New York, N.Y., p. 120:
W. J. MacKnight et al., in Polymer Blends; D. R. Paul and S. Newman, eds., 1978, published by Academic Press, New York, N.Y., state on page 188:
In this passage, it is clear from the omitted text, that by compatibility the authors mean miscibility, i.e., single..phase behavior. See, for example, the discussion in Chapter 1 by D. R. Paul in the same work.
As a specific example of how difficult it is to predict the miscibility of polymers, a priori let us take an example from U.S. Pat. No. 4,258,155. Example 8 shows that the polyamideimide ##STR2## and the polyetherimide ##STR3## are miscible as evidenced by the single Tg of the blends. However, as described in European Patent Application 016,354, the closely related polyamide-imide copolymer (5) ##STR4## is not miscible with the polyetherimide (4) above even though it contains 50 mole percent of repeat units (3).